From both a fundamental viewpoint and the perspective of wave-function engineering of an electron pumped by single-electron sources, it is important to understand how an electron gains energy while propagating along a time-dependent region in a quantum Hall channel. In our previous work, we experimentally observed that, when the electron travels through the time-dependent region before entering the pump, the pump current becomes substantially larger than the quantized value. We here present the results of a theoretical and experimental investigation of the mechanism underlying the heating of electrons traveling through a region of time-dependent potential induced by an rf signal. Using the Floquet scattering theory, we describe the energy distribution of the heated electrons, whose effective temperature can be substantially larger than the cryostat temperature. The behavior of the measured currents when the barrier height and the radio-frequency power are varied is in good qualitative agreement with the theoretical predictions.